docs: def sxform(instring, tostring, et):
      """
      Return the state transformation matrix from one frame to
      another at a specified epoch.
  
      http://naif.jpl.nasa.gov/pub/naif/toolkit_docs/C/cspice/sxform_c.html
  
  
      :param instring: Name of the frame to transform from.
      :type instring: str
      :param tostring: Name of the frame to transform to.
      :type tostring: str
      :param et: Epoch of the state transformation matrix.
      :type et: Union[float,Iterable[float]]
      :return: A state transformation matrix.
      :rtype: 6x6-Element Array of floats
      """
      instring = stypes.stringToCharP(instring)
      tostring = stypes.stringToCharP(tostring)
      xform = stypes.emptyDoubleMatrix(x=6, y=6)
      if hasattr(et, "__iter__"):
          xforms = []
          for t in et:
              libspice.sxform_c(instring, tostring, ctypes.c_double(t), xform)
              checkForSpiceError(None)
              xforms.append(stypes.cMatrixToNumpy(xform))
          return xforms
      else:
          et = ctypes.c_double(et)
          libspice.sxform_c(instring, tostring, et, xform)
          return stypes.cMatrixToNumpy(xform)